Various components of a wind turbine, including components arranged in or near the nacelle, such as drive train, main shaft, generator, main bearing or hub, sometimes require maintenance, repair or replacement. It is therefore necessary to allow maintenance personnel to gain access to these parts in order to allow them to perform the required maintenance, repair or replacement. This will sometimes include gaining access to an interior part of the hub. For safety reasons the rotor must be prevented from performing rotational movements during such maintenance operations.
A number of locking arrangements have previously been suggested in order to provide a suitable locking of the rotor against rotational movements. WO 2008/059088 A1 discloses an adjustable, self-aligning rotor locking device for an aerogenerator, comprising a rotor, a nacelle structure housing power generating means coupled to the hub of the rotor, braking means and means for controlling the rotational position of the power train. The nacelle structure and the hub of the rotor are arranged so as to prevent the rotor hub from rotating during certain maintenance and assembly operations. The arrangement includes at least one mobile pin in the nacelle, actuation means for pushing/pulling the pin axially in relation to at least one corresponding hole in the hub.
EP 1 291 521 A1 discloses a wind turbine comprising a nacelle on a tower. The wind turbine is provided with a rotor lock device for locking a rotor disk and fixation means for fixing the rotor disk to the nacelle. The rotor lock device comprises an axially movable pin arranged on the nacelle structure and corresponding apertures formed in the rotor disk.
Thus, WO 2008/059088 A1 and EP 1 291 521 A1 both disclose rotor locking arrangements in which a movable member is moved along a substantially axial direction between a position in which the rotor is locked against rotational movements and a position in which the rotor is allowed to perform rotational movements. A disadvantage of such an arrangement is that it is not possible to use the locking mechanism directly for absorbing tilt or yaw loads, e.g. in the case that the support for the main shaft, or the main shaft itself, needs to be removed during the maintenance operation. Another disadvantage is that it is difficult and relatively expensive to manufacture the hub in a manner which allows the axial movement of the locking parts.
EP 1 617 075 A1 discloses a method and an apparatus for changing a transmission of a wind power installation. The rotor shaft is supported on the machine frame during the transmission change operation by means of a support at the transmission side so that the rotor is permitted to remain on the rotor shaft during the transmission change. The support is a yoke which is mounted between the rotor shaft and the machine frame immediately prior to the transmission change and is removed again immediately after the transmission change. In the case that the drive train is suspended in the nacelle by means of a so-called three point suspension, the yoke supports the main shaft when the gear is removed during a replacement operation, thereby removing part of the normal support of the drive train. The yoke may further prevent the main shaft from performing rotational movements, due to friction between the yoke and the main shaft. However, this rotational locking is too unreliable to be used as a safety measure during maintenance operations.